Rear eject body for off-highway haulage units

ABSTRACT

A rear eject body for a truck is provided. The body includes a floor and a pair of opposing sidewalls. A tailgate extends between the opposing sidewalls at a rear end of the rear eject body. The tailgate is pivotally supported for movement between an open position and a closed position. An ejector is supported in the rear eject body for movement between a retracted position at a forward end of the body and an extended position at the rear end of the body. A tailgate actuation assembly moves the tailgate between the open and closed positions in response to movement of the ejector between the retracted and extended positions. An ejector guide assembly includes sleds that slide in guide tracks to thereby guide the ejector as the ejector moves between the retracted and extended positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication 60/359,359, filed Feb. 25, 2002, U.S. Provisional PatentApplication 60/365,328, filed Mar. 18, 2002 and U.S. Provisional PatentApplication 60/424,169 filed Nov. 6, 2002.

FIELD OF THE INVENTION

This invention pertains to haulage units, in particular off-highwayhaulage units with open top, top loaded rear eject bodies.

BACKGROUND OF THE INVENTION

Off-highway trucks equipped with rear eject bodies are used to haul anddump materials in haulage applications such as mines, construction sitesand landfills. Rear eject bodies have a number of advantages overconventional rear dump bodies. For example, rear eject bodies typicallyare self-cleaning thereby minimizing carry back of sticky materials.Additionally, this style of body allows dumping on the go, increasingtruck productivity. Dumping on the go also minimizes the need foradditional support equipment to spread and level the dumped material.With regard to the dumping of materials, rear eject bodies allowmaterials to be dumped on steeper slopes and in areas where there issoft truck underfoot conditions. Moreover, trucks with rear eject bodiescan dump their loads in areas with overhead wires and bridges as well asin tunneling applications.

In contrast to conventional rear dump bodies which are pivoted into araised position for dumping, rear eject bodies use an ejector blade thatis moved horizontally from the front end to the rear end of the truckbody by one or more hydraulic cylinders to eject and dump material fromthe truck body. Since the body does not have to be raised for dumping,rear eject bodies are particularly suited for haulage applications inwhich there is limited overhead dump clearance (e.g., because of wires,bridges, tunnels, and trees), underground haulage application or haulageapplication where ground instability makes raising a dump body to thedumping position extremely hazardous. Additionally, rear eject bodiesdump materials in a more controlled manner. For example, a rear ejectbody can dump material while the truck is still moving in order tospread the dumped material over a larger area. Dumping material whilethe truck is on the go also speeds the dumping process. The use of theejector blade also enables rear eject bodies to handle hard-to-dumpsticky materials such as dirt and clay mixtures which hang-up and oftendo not flow out of conventional raised rear dump bodies.

In general, rear eject bodies are well known on both off-highway trucksand street legal refuse trucks. Unfortunately, many commerciallyavailable rear eject bodies have a number of drawbacks. For example,since typical rear eject bodies have a number of moving parts requiringregular lubrication and maintenance, they can be costly andtime-consuming to maintain. Moreover, because large hydraulic cylindersare required to move the ejector blade, rear eject bodies can be quiteexpensive. Some rear eject bodies also use additional hydrauliccylinders to operate the tailgate, further increasing the cost. Manyrear eject bodies also dump material relatively slowly, increasing dumpcycle times and lowering productivity.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a rear eject body for a truck. The bodyincludes a floor and a pair of opposing sidewalls. A tailgate extendsbetween the opposing sidewalls at a rear end of the rear eject body andis pivotally supported for movement between an open position and aclosed position. An ejector blade is supported in the rear eject bodyfor movement between a retracted position at a forward end of the bodyand an extended position at the rear end of the body.

According to one embodiment of the invention, a tailgate actuationsystem moves the tailgate between the open and closed positions inresponse to movement of the ejector blade between the retracted andextended positions. The tailgate actuation system links the tailgate andthe ejector blade when the ejector blade is in the closed positionthereby holding the tailgate in the closed position. The tailgateactuation system releases the tailgate from the ejector blade as theejector blade moves from the retracted position towards the extended ormaterial ejection position such that the tailgate can swing freely intothe open position. The tailgate actuation system then reestablishes thelink between the tailgate and the ejector blade as the ejector blademoves from the extended position back to the retracted position therebypulling the tailgate from the open position back into the closedposition. The tailgate actuation system can further include a flexiblelink connected to the tailgate that acts around a drum for pulling thetailgate from the open to the closed position. The drum can have aradius of curvature that varies such that the moment arm on which theflexible link acts with respect to the tailgate is greatest when thetailgate is in a horizontal position and relatively less when thetailgate is in the more vertical open and closed positions.

According to another embodiment of the invention, the rear eject bodyincludes an ejector blade guide assembly. The ejector blade guideassembly includes a plurality of sleds connected to the ejector blade.Each sled is received in one of a pair of guide tracks or slides. Eachguide track or slide is arranged on an inside surface of a respectiveone of the sidewalls, wherein the sleds move in guide tracks or slidesand thereby guide the ejector blade as the ejector blade moves betweenthe retracted and extended positions.

According to another embodiment of the invention, the rear eject bodycan include a hydraulic cylinder for moving the ejector blade betweenthe retracted and extended positions. The hydraulic cylinder isconfigured to extend and thereby move the ejector blade towards theextended position when hydraulic fluid is supplied to an extend side ofthe hydraulic cylinder and to retract and thereby move the ejector bladetowards the retracted position when hydraulic fluid is supplied to aretract side of the hydraulic cylinder. The rear eject body can furtherinclude a hydraulic control system for controlling the flow of hydraulicfluid to and from the extend and retract sides of the hydrauliccylinder. When hydraulic fluid is supplied to the extend side of thehydraulic cylinder, the hydraulic control system can be configured so asto build backpressure into the retract side of the hydraulic cylinderbefore hydraulic fluid is allowed to flow to the extend side of thehydraulic cylinder to initiate extension of the hydraulic cylinder. Thehydraulic control system could also be configured to allow hydraulicfluid flow out of the extend side of hydraulic cylinder through a lineconnecting the extend side of the hydraulic cylinder directly to ahydraulic fluid tank or reservoir when hydraulic fluid is being suppliedto the retract side of the hydraulic cylinder during retraction of thehydraulic cylinder when the pressure in the retract side of thehydraulic cylinder reaches a predetermined value.

According to another embodiment of the present invention, the rear ejectbody can include a hydraulic cylinder for moving the ejector bladebetween the retracted and extended positions and a mounting arrangementfor connecting the barrel of the hydraulic cylinder to the ejectorblade. The mounting arrangement defines a vertical pivot axis aboutwhich the ejector blade can pivot slightly relative to the hydrauliccylinder as the ejector blade is extended and retracted. The verticalpivot axis is located at a rearward end of the hydraulic cylinder barrelthat is furthest from the rod end of the hydraulic cylinder. Themounting arrangement can further include a trunnion mount that defines ahorizontal pivot axis about which the ejector blade and hydrauliccylinder can pivot relative to each other. The horizontal pivot axis islocated at a forward end of the hydraulic cylinder barrel nearest therod end of the cylinder.

According to another embodiment of the present invention, the ejectorblade can have a lower face that angles upward away from the floor asthe lower face extends toward the front end of the body, an upper facethat angles downward toward the floor as the upper face extends towardthe front end of the body and a pair of opposing side faces wherein eachside face angles inward away from the sidewalls as the side face extendstowards the front end of the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an articulated off-highway truck having anexemplary rear eject body constructed in accordance with the presentinvention showing the ejector blade retracted and the tailgate closed.

FIG. 2 is a rear view of the truck and rear eject body of FIG. 1 showingthe ejector blade retracted and the tailgate closed.

FIG. 3 is a side view of the truck and rear eject body of FIG. 1 showingthe ejector blade extended and the tailgate open.

FIG. 4 is a rear view of the truck and rear eject body of FIG. 2 showingthe ejector blade extended and the tailgate open.

FIG. 5 is a perspective view of the rear eject body of FIG. 1 showingthe ejector blade retracted and the tailgate closed.

FIG. 6 is a perspective view of the rear eject body of FIG. 1 showingthe ejector blade extended and the tailgate open.

FIG. 7 is a front view of the rear eject body of FIG. 1.

FIG. 8 is a front perspective view of the rear eject body of FIG. 1showing the ejector blade extended and the tailgate open.

FIG. 9 is an enlarged partial end view of the rear eject body of FIG. 1showing one of the ejector guide tracks/slides.

FIG. 10 is an enlarged partial end view of the rear eject body of FIG. 1showing one of the ejector guide tracks and one of the ejector bladesleds with the ejector blade cutaway.

FIG. 11 is an enlarged end view of an alternative guide track/slide andsled arrangement for the rear eject body of the present invention.

FIG. 12 is an enlarged partial side perspective view of the rear ejectbody of FIG. 1 showing the inclined section of one of the guide tracksat the forward end of the rear eject body which helps retain the ejectorblade in the retracted position.

FIG. 13 is an enlarged partial side perspective view of a rear ejectbody according to the present invention having an alternative guidetrack with a flat section of guide track in front of the inclinedsection at the forward end of one of the guide tracks which helps retainthe ejector blade in the retracted position.

FIG. 14 is a partial perspective view of the rear eject body of FIG. 1with a portion of one of the body sidewalls cutaway so as to show thetailgate actuation system.

FIG. 15 is an enlarged perspective view of the ejector blade andtailgate actuation system of the rear eject body of FIG. 1 showing theejector blade in the fully retracted position.

FIG. 16 is a perspective view of the ejector blade and tailgateactuation system of the rear eject body of FIG. 1 showing the ejectorblade in the fully retracted position and the tailgate closed.

FIG. 17 is a perspective view of the ejector blade and tailgateactuation system of the rear eject body of FIG. 1 showing the ejectorblade after it has started moving rearward towards the extended or ejectposition and the tailgate in the open position.

FIGS. 18-28 are enlarged partial top plan views of the ejector blade andtailgate actuation system of the rear eject body of FIG. 1 showing thesequence of operation of the tailgate actuation system as the ejectorblade moves from the fully retracted position to the extended positionand back to the fully retracted position. The direction of travel of theejector blade is indicated by the respective arrows; in FIGS. 18-24, theejector blade is extending or moving to the rear of the rear eject body;while in FIGS. 25-28, the ejector blade is retracting or moving to thefront of the rear eject body.

FIG. 29 is an enlarged partial side view of the rear eject body of FIG.1 showing the tailgate in the nearly vertical or closed position.

FIG. 30 is an enlarged partial side view of the rear eject body of FIG.1 showing the tailgate in a horizontal position between the closed andopen positions.

FIG. 31 is an enlarged partial side view of the rear eject body of FIG.1 showing the tailgate in the nearly open position.

FIGS. 32 a-c are partial side views of the tailgate actuation system andtailgate of the rear eject body of FIG. 1 showing the chain and chaindrum as the tailgate moves between the closed and open positions.

FIG. 33 is an enlarged partial side view of a rear eject body accordingto the present invention which has an alternative chain drumconfiguration showing the tailgate in the closed position.

FIG. 34 is an enlarged partial side view of the rear eject body of FIG.33 showing the tailgate in the nearly open position.

FIG. 35 is an enlarged front perspective view of the rear eject body ofFIG. 1 showing the hydraulic cylinder mounting arrangement.

FIG. 36 is an enlarged front perspective view of the rear eject body ofFIG. 1 showing the hydraulic cylinder mounting arrangement.

FIG. 37 is an enlarged partial side view of a rear eject body accordingto the present invention which has an alternative tailgate pivotarrangement showing the tailgate in the closed position.

FIG. 38 is an enlarged partial side view of the rear eject body of FIG.37 showing the tailgate in the open position.

FIG. 39 is an enlarged partial perspective view showing the forward endof one of the body sidewalls and the various mounting positions for thequick release dog of the tailgate actuation system.

FIG. 40 is a schematic drawing of a hydraulic control system for thehydraulic cylinder of the rear eject body of FIG. 1 with the hydrauliccylinder being extended. The arrows indicate direction of hydraulicfluid flow into and out of hydraulic control system.

FIG. 41 is a schematic drawing of the hydraulic control system of FIG.37 with the hydraulic cylinder being retracted. The arrows indicatedirection of hydraulic fluid flow into and out of the hydraulic controlsystem.

FIG. 42 is a schematic drawing of an alternative hydraulic controlsystem for the hydraulic cylinder that also controls tailgate cylinderswhich could be used to move the tailgate between the open and closedpositions.

FIG. 43 is a schematic drawing of an alternative hydraulic controlsystem for the hydraulic cylinder which also controls tailgate cylinderswhich could be used to move the tailgate between the open and closedpositions with the addition of a pressure operated check valve in thetailgate close circuit.

DETAILED DESCRIPTION OF THE INVENTION

Referring now more particularly to the drawings, there is shown in FIGS.1-4 an illustrative off-highway truck 10 having a rear eject body 12constructed in accordance with the teachings of the present invention.The illustrated rear eject body 12 consists of a floor 13, two sidewalls14, tailgate 16, and an ejector blade 18. The ejector blade 18 whenactuated pushes a load in the rear eject body 12 from the front of therear eject body out the rear of the rear eject body. In particular, theejector blade 18 is moved from a body loaded or fully retracted positionat the front of the rear eject body 12 (see, e.g., FIGS. 1, 2, 5 and 7)to a body empty or fully extended position at the rear of the rear ejectbody 12 (see FIGS. 3, 4, 6 and 8) by, in this case, a multi-stagedouble-acting hydraulic cylinder 20. As used herein, the terms “front”and “forward” and “rear” and “rearward” are used with respect to thetruck cab 21 being at the front end of the truck 10 and the tailgate 16being at the rear end of the truck 10 (see FIGS. 1 and 3).

In the illustrated embodiment, the ejector blade 18 generally includes aframe 22 (see FIGS. 6-8) that supports an ejector plate 24. As shown inFIGS. 4-6, the ejector plate 24 is oriented so as to face towards therear end of the rear eject body 12 and extends between the sidewalls 14of the rear eject body 12 and upwards from the floor 13 of the reareject body 12 to a distance above the upper edges of the sidewalls 14.The illustrated ejector plate 24 includes an upper face 25, a lower face26 and a pair of opposing side faces 27. To pull material away from thesidewalls 14 and direct it towards the center of the rear eject body 12,each of the side faces 27 of the ejector plate 24 angles inward towardsthe center of the body 12 as it extends forward toward the front end ofthe rear eject body 12. The lower face 26 of the ejector plate 24 anglesupward away from the body floor 13 as it extends forward toward thefront end of the rear eject body 12 to help lift material up andsomewhat off the body floor 13. The upper face 25 of the ejector blade24, in turn, angles downward towards the body floor 13 as it extendsforward toward the front end of the rear eject body 12. Thisconfiguration helps prevent material from tumbling over the top of theejector plate 24 when it is pushing material rearward.

To guide the ejector blade 18 as it moves between the body loaded orfully retracted position at the front of the rear eject body 12 and thebody empty or fully extended position at the rear of the rear eject body12, the ejector blade 18 includes a guide assembly 28 (see FIG. 10).Typically, conventional ejector blades ride on rollers or cam followersas they move between the front and rear of the truck body.Unfortunately, these rollers and cam followers require regularmaintenance and lubrication. In contrast, with one embodiment of thepresent invention, the guide assembly 28 for the ejector blade 18 caninclude sleds 30 (see, e.g., FIGS. 7, 10 and 15) that are received andslide in corresponding guide tracks 32 (see, e.g., FIGS. 7-10) arrangedalong the sidewalls 14 of the rear eject body 12. Unlike conventionalrollers and cam followers, the sleds 30 and guide tracks 32 do not haveany lubrication points, thereby substantially reducing the requiredmaintenance for the ejector blade 18.

One guide track 32 is arranged along the inner side of each of the twosidewalls 14 of the rear eject body 12 (one of the tracks can be seen inFIGS. 9 and 10 and both can be seen in FIG. 7). In the illustratedembodiment, the ejector blade 18 has two sleds 30 on each side of theejector blade frame 22 with one side being shown in FIG. 15. These sleds30 are positioned near the four bottom corners of the ejector blade 18.Each sled 30 is supported on the end of a respective threaded rod 34(FIGS. 10-11) that is received in a corresponding threaded tube on theejector blade 18. The use of the threaded rods 34 allows the position ofthe sleds 30 to be adjusted relative to the ejector blade 18 therebyensuring a good fit.

To facilitate sliding of the sleds 30 in the guide tracks 32, the sleds30 can be made of or plated with a hardened steel material.Additionally, the guide tracks 32 in which the sleds 30 ride can also belined or made out of a very hard steel material such as the samematerial used for the sleds 30. In particular, the three sides of theguide track 32 (i.e., outside, upper and lower walls of the track—seeFIG. 10) can be either lined or made of a very hard steel material. Twoexamples of steel materials that are suitable for use in constructingthe sleds 30 and guide tracks 32 are Hadfield manganese steel, which isa 11-14% manganese steel, and the fused alloy steel plate sold under thetradename Arcoplate by Alloy Steel International, Inc. of 42 MercantileWay P.O. Box 3087 Malaga DC 6945, Western Australia. Arcoplate wearplate consists of a chromium carbide rich (+/−60%) steel alloy overlayon a mild steel backing. Additional information regarding the Arcoplatematerial can be found at www.arcoplate.com.au. One example of a suitableHadfield manganese steel is the wear-resistant high manganese steel soldunder the tradename Manganal by Stulz Sickles Steel Company ofElizabeth, N.J. Manganal is a high manganese austentitic, work hardeningsteel that typically is 12-14% manganese and 1.00-1.25% carbon.Additional information regarding the Manganal material can be found atwww.stulzsicklessteel.com. The Hatfield manganese and Arcoplatematerials are very hard such that each can operate against itselfwithout galling.

To help ensure that the guide tracks 32 remain clear of debris, thesleds 30 and guide tracks 32 can be configured such that as the sleds 30move between the front and rear of the rear eject body 12, debris iscleaned out of the tracks. Specifically, in the illustrated embodimentas shown in FIG. 15, each of the sleds 30 has a tapered configuration atboth its front and end rear end that allows the sleds 30 to scrapedebris away from the walls of the guide track 32 and direct the debrisback towards the center of the rear eject body 12 as they move betweenthe front and rear ends of the rear eject body 12. In this case, theforward end of each sled 30 includes upper and lower edges 36 (only theupper edge can be seen in FIG. 15) that angle inward and away from thebody sidewalls 14 as the edges extend forward. Similarly, the rear endof each of the sleds 30 includes upper and lower edges 38 (only theupper edge can be seen in FIG. 15) that angle inward and away from thebody sidewalls 14 as the edges extend rearward.

To further facilitate cleaning of the guide tracks 32, the guide tracks32 can be configured so as to have a bottom wall 40 angling downward andinward toward the center of the rear eject body 12 as it extends awayfrom the body sidewall 14 as shown, for example, in FIGS. 9 and 10. Whenthe sleds 30 slide back and forth in the guide tracks 32, the debristhat is dislodged by the sleds 30 falls onto the bottom wall 40 of theguide track 32. Because it is set at an angle, the debris that falls onto the bottom wall 40 of the track 32 slides or is otherwise directedout of the guide track 32 and towards the center of the rear eject body12. In the embodiment illustrated in FIGS. 9 and 10, the guide tracks 32are also elevated a distance above the body floor 13. The elevation ofthe guide tracks 32 creates space for any debris that is expelled fromthe guide tracks 32. Alternatively, the guide tracks 32 could bearranged so as to be level with the body floor 13 as shown in FIG. 11.

To help prevent the ejector blade 18 from drifting rearward when therear eject body 12 is empty, such as when the truck 10 is driven from adump point back to a loading point, each of the guide tracks 32 can beconfigured with an incline near its forward end that the correspondingsleds 30 have to travel up when the ejector blade 18 first starts movingrearward. In the embodiment illustrated in FIG. 12, a short inclinedtrack section 42 is provided in the bottom wall 40 at the forward end ofeach guide track 32. Each inclined track section 42 angles downward asit extends toward the forward end of the guide track 32. This downwardangle creates a recess in which the forward sled 30 on each side of theejector blade 18 rests when the ejector blade 18 is in the fullyretracted position. Since these forward ejector blade sleds 30 musttravel up the inclined track sections 42 in order to move rearward, theejector blade 18 is essentially held by gravity at the forward end ofthe rear eject body 12 when the hydraulic cylinder 20 is retracted. Inan alternative embodiment, a, recessed flat track section 44 can beprovided at the forward end of each guide track 32 as shown in FIG. 13.This recessed flat track section 44 is joined to the remainder of theguide track 32 by an inclined track section 42 that angles upward as itextends rearward in order to provide resistance to any rearward drift ofthe ejector blade 18. The recessed, flat track section 44 permits thesleds 30 to be oriented parallel to the ground when the ejector blade 18is fully forward. The inclined track section 42 shown in FIG. 13 is at aslightly steeper angle than the inclined track section 42 of FIG. 12. Asa result, the inclined track section 42 of FIG. 13 offers moreresistance to any rearward drift of the ejector blade 18.

To reduce the friction associated with ejecting material from the reareject body 12, the floor 13 of the rear eject body 12 can be lined witha material having a low coefficient of friction as compared toconventional steel plate. Using a material with a relatively lowcoefficient of friction reduces the amount of force necessary to ejectmaterial from the rear eject body 12. As a result, a relatively smallerhydraulic cylinder 20 can be used to move the ejector blade 18 therebyreducing the cost of the rear eject body 12. The use of a lowcoefficient of friction material also results in a relatively fastermovement of the ejector blade 18 between the retracted and extendedpositions. Two examples of suitable materials for lining the body floor13 are Hadfield manganese steel and the wear plate sold under theArcoplate tradename mentioned above. As noted above, both Hadfieldmanganese steel and Arcoplate wear plate are extremely hard, and whenpolished, have an extremely low coefficient of friction. Advantageously,these materials are also very resistant to abrasion and wear caused bymaterial sliding across the body floor 13.

To allow the illustrated rear eject body 12 to be easily mounted toexisting trucks that are configured to receive a pivotable dump body,the rear eject body 12 can be configured to be mountable to the standardtruck chassis dump body pivot mounts. In particular, as best shown inFIGS. 1, 2 and 5, a pair of mounting brackets 46 are provided on theunderside of the body floor 13 adjacent the rear end thereof. Wheninstalling the rear eject body 12, these mounting brackets 46 can beconnected to the dump body pivot mounts 48 that are typically providedon a truck chassis configured to receive a pivotable dump body such asin the illustrated embodiment (see, e.g., FIGS. 1 and 2). Alternatively,the dump body pivot mounts 48 on the truck chassis could also be used asthe pivot points for the tailgate 16 such as shown in FIGS. 37 and 38.

To control movement of the tailgate 16 between the open and closedpositions so that the load can be ejected out of the body, theillustrated rear eject body 12 includes a tailgate actuation system 50(best shown, for example, in FIGS. 14-28). Advantageously, unlike manyrear eject bodies that use separate hydraulic cylinders at the rear ofthe body to move the tailgate, the tailgate actuation system 50 utilizesa single hydraulic cylinder 20 to operate both the ejector blade 18 andtailgate 16. This reduces the required maintenance as well as the costof the rear eject body 12 by eliminating the additional hydrauliccylinders, hydraulic lines and hydraulic controls conventionallyassociated with operating the tailgate. The tailgate actuation system 50links movement of the tailgate 16 to movement of the ejector blade 18helping to ensure that the tailgate 16 opens quickly and reliably duringdumping. In particular, the actuation of the ejector blade 18 from thefully retracted position to a partially extended position controls theopening and closing of the tailgate 16 at the rear of the rear ejectbody 12.

In the illustrated embodiment, the tailgate actuation system 50 includesa release rod 52 to which a chain 54 is attached as shown in FIGS. 14,16 and 17. The chain 54, in turn, wraps around a chain drum 55 andconnects to the tailgate 16. Specifically, in the illustratedembodiment, the chain 54 is connected to the chain drum 55 using a chaintensioner 57 (FIGS. 2, 5, 16, 29, 30 and 32), which is adjustable via alarge nut on a threaded rod to ensure that the tailgate 16 fits tightlyagainst the sidewalls 14 of the rear eject body 12 when in the closedposition. A tailgate release lever 58 is pivotally mounted on theforward end of the release rod 52. The tailgate release lever 58, rod 52and chain 54 assembly extends along the outside surface of one or bothof the plates of the sidewalls 14 of the rear eject body 12 such asshown in FIG. 14 (for the sake of clarity the outer structure of thesidewall 14 is removed in FIG. 14).

With the ejector blade 18 fully retracted, the tailgate 16 is heldclosed by the engagement of the tailgate release lever 58 with a stopsurface 60 on the ejector blade 18 (see FIGS. 15, 16, and 18). As theejector blade 18 starts to move rearward in order to eject a load, therelease rod 52 starts to slide rearward (pulled by the weight of thetailgate 16) and engages a quick release dog 62 which is pivotallysupported via a pair of mounting ears 63 on the sidewall 14 of the reareject body 12. The engagement of the tailgate release lever 58 with thequick release dog 62 pivots the gate release lever 58 in a clockwisedirection (with respect to the drawings) relative to the release rod 52(see FIG. 19). This disengages the tailgate release lever 58 from thestop surface 60 on the ejector blade 18 (see FIGS. 20 and 21). Therelease rod 52 then slides rearward until a notch 64 on the release rod52 engages a stop surface 66 provided in the sidewall 14 of the reareject body 12 (see FIG. 22). At this point, the tailgate 16 has swunginto the fully open position.

As the ejector blade 18 continues to move rearward to eject the load,the ejector blade 18 again engages the tailgate release lever 58. Thispivots the tailgate release lever 58 in the clockwise direction so thatthe ejector blade 18 can pass by the tailgate release lever 58 (see FIG.23). Once the ejector blade 18 is past the tailgate release lever 58, aspring 68 which extends between the tailgate release lever 58 and therelease rod 52 pivots the tailgate release lever 58 back into a positionwherein the tailgate release lever 50 extends perpendicularly relativeto the release rod 52 (see FIG. 24).

As the ejector blade 18 moves back to the fully retracted position, thestop surface 60 on the ejector blade 18 once again engages the tailgaterelease lever 58, in this case, when the ejector blade 18 isapproximately 80% of the way back to the retracted position (see FIG.25). The release rod 52 is configured to prevent the tailgate releaselever 58 from pivoting past perpendicular in the counter-clockwisedirection relative to the release rod 52. Accordingly, when the ejectorblade 18 engages the tailgate release lever 58 as the ejector blade 18returns to the fully retracted position, it pulls the release rod 52 andchain 54 forward (see FIG. 26) and thereby rotates the tailgate 16 backinto the closed position. The quick release dog 62 on the sidewall 14 ofthe rear eject body 12 is pivotal so that the tailgate release lever 58can move forward past the quick release dog 62 into the fully retractedand closed position (see FIGS. 27, 28 and 18). A spring 70 then pivotsthe quick release dog 62 inward or clockwise back behind the gaterelease lever 58 (see FIG. 18).

Advantageously, when a load is being ejected, the tailgate 16 isreleased and is fully open after very minimal rearward movement of theejector blade 18 so that the load can be ejected from the rear ejectbody 12 (e.g., after approximately six inches rearward movement of theejector blade 18). In the embodiment illustrated in FIGS. 14-28, theejector blade 18 only needs to move approximately 3-5% of the totalejector blade 18 rearward movement to fully release the tailgate 16. Incontrast, 17-25% of the total ejector blade 18 forward or retractionmovement is used to move the tailgate 16 into the closed position.

As best shown in FIGS. 12, 13 and 39, the rear eject body 12 can beconfigured so that the quick release dog 62 that allows for “quick”release of the tailgate 16 can be positioned in any one of a pluralityof positions. This permits adjustment of the rearward distance theejector blade 18 moves before the tailgate 16 is released to fully open.In this case, the quick release dog 62 can be positioned in one of fourdifferent positions each of which is a different distance from theforward end of the rear eject body 12. Mounting holes for a plate whichcarries the mounting ears 63 for the quick release dog 62 are providedat each of the mounting positions. A corresponding cutout 72 in thesidewall 14 of the rear eject body 12 is provided for each of themounting positions (the cutout for the second mounting position from thefront is covered by the mounting ears plate in FIG. 39). These cutouts72 provide the openings through which the quick release dog 62 wouldoperate to release the tailgate 16 at the various release points.Positioning the quick release dog 62 in the mounting ears 63 closest tothe forward end of the rear eject body 12 releases the tailgate 16 tothe fully open position the quickest, i.e. after the shortest movementof ejector blade 18. In contrast, positioning the quick release dog 62in the mounting ears 63 furthest from the forward end of the rear ejectbody 12 releases the tailgate 16 to the fully open position the slowest,i.e. after the greatest movement of the ejector blade 18 and after thetailgate 16 has already pivoted, as a result of the ejector blademovement, a significant distance towards the open position.

To reduce the force that has to be applied to the ejector blade 18 torotate the tailgate 16 from the open to the closed position, thetailgate actuation system 50 can be configured so as to vary the torqueapplied to the tailgate 16 as the tailgate 16 moves between the open andclosed position. When closing the tailgate 16, the amount of forcerequired to move and close the tailgate 16 is greatest when the tailgate16 is in a horizontal position. Once past the horizontal position, theamount of force required to move the tailgate 16 decreases as thetailgate 16 approaches a vertical position over the tailgate pivot point73. In the embodiment illustrated in FIGS. 29-32, the varying of thetorque is achieved by providing a chain drum 55 having a varying radiussuch that the moment arm acting on the tailgate 16 from the retractionof the ejector blade 18 varies depending on the tailgate position. Themoment arm is the perpendicular distance between the line of action(force) created by the ejector blade acting on release rod 52 and thetailgate pivot point 73. The chain drum 55 provides a curved surfacearound which the chain 54 acts to apply a moment or torque on thetailgate 16. The chain drum includes a first end that is slidablyreceived in the sidewall 14 of the rear eject body 12 and a second endthat is connected to the tailgate 16. In this case, the radius ofcurvature of the chain drum 55 varies between the first and second endsof the drum such that distance between the chain's line of action andthe tailgate pivot point 73 varies depending on the position of thetailgate. Specifically, as best shown in FIG. 32, the radius ofcurvature of the chain drum 55 varies such that the radius of actuationor moment arm on which the chain 54 acts to rotate the tailgate 16 isgreatest (i.e., the chain's line of action is the furthest distance fromthe tailgate pivot point 73) when the tailgate 16 is in a horizontalposition and the greatest torque is required to rotate the tailgate 16.In turn, the moment arm on which the chain 54 acts is less (i.e., thechain is a relatively shorter distance from the tailgate pivot) when thetailgate 16 is being held in the closed position and when it firststarts leaving the fully open position because less torque is requiredto rotate the tailgate 16 as it is just beginning to leave the fullyopen position.

In an alternative embodiment, the chain drum 55 could be arranged andconfigured such that it has a constant radius of actuation but has acenter of rotation that is different than the tailgate pivot point 73 asshown in FIGS. 33 and 34. With this arrangement, the smallest moment armfor the chain 54 is provided when the tailgate 16 is in the fully openposition and the greatest moment arm for the chain 54 is provided whenthe tailgate 16 is nearly fully closed. Accordingly, less force wouldhave to be applied to the chain 54 in order to hold the tailgate 16 inthe closed position.

To prevent any twisting movement of the ejector blade 18 from inducingforces into the hydraulic cylinder 20, a hydraulic cylinder mountingarrangement can be provided which permits movement of the ejector blade18 relative to the hydraulic cylinder 20. In the illustrated embodiment,the hydraulic cylinder mounting arrangement comprises a cylindertrunnion mount 74 as best shown in FIGS. 35 and 36. The cylindertrunnion mount 74 is provided at the forward or rod end of the cylinderbarrel 75 of the hydraulic cylinder 20 in order to counterbalance theweight of the cylinder barrel 75 and extended cylinder rod at fullhydraulic cylinder extension. The cylinder trunnion mount 74 includes acollar 76 that surrounds the hydraulic cylinder barrel 75. A pair ofstub shafts 78 protrude from the collar 76 and are received in a pair oflaterally spaced apart plates 80 that are supported on the ejector frame22. This arrangement allows the hydraulic cylinder 20 to pivot up anddown relative to the ejector blade 18. Additionally, the ejector blade18 may rack or twist slightly side-to-side as it slides back and forthin the rear eject body 12 (e.g., less than an inch on either side of theejector blade 18). To account for this movement, the cylinder mountingarrangement also has a vertical axis of rotation. In particular, as bestshown in FIG. 36, the laterally spaced plates 80 to which the hydrauliccylinder 20 is mounted are connected at their rearward upper and lowerends to a respective pair of vertically extending pivots 82 that aresupported on the ejector blade frame 22. These pivots 82 permit thehydraulic cylinder 20 (along with the laterally spaced plates 80) torotate about a vertical axis defined by the two pivots 82. If the twopivots 82 are arranged so that the vertical axis of rotation is locatedat or near the neutral point of any side-to-side twisting of the ejectorblade 18, side-to-side twisting of the hydraulic cylinder 20 isvirtually eliminated. In this case, the vertical axis defined by the twopivots 82 is arranged at the rearward end of the hydraulic cylinderbarrel. With this arrangement, the hydraulic cylinder 20 pulls on theejector blade 18 as it extends or ejects the load in such a way as toproduce a centering action on the ejector blade 18.

The illustrated rear eject body 12 can further include a hydrauliccontrol system such as shown in FIGS. 40 and 41. The illustratedhydraulic control system controls extension and retraction of thehydraulic cylinder 20 and, in particular, prevents misfiring of thecylinder. The misfire phenomena in double-acting, multi-stage telescopiccylinders can occur on cylinder extension when one of the smallerdiameter stages is partially extended out of sequence, blocking theretract oil flow out of a larger diameter stage back to tank on theretract side of the hydraulic cylinder. It is a phenomenon that iswell-known to manufacturers of multi-stage, double-acting telescopiccylinders. By creating a positive backpressure on the hydraulic cylinder20 retract segments or in the retract pressure line as the hydrauliccylinder 20 is extended, the hydraulic control system 84 of the presentinvention keeps the multi-stage telescopic sections of the hydrauliccylinder 20 in sequence and prevents misfiring of the cylinder.

The flow of oil to the hydraulic control system can be controlled, forexample, by the conventional 3-position, 4-way hydraulic valve that istypically provided on the type of off-highway trucks on which the reareject body 12 could be installed. The operation of the hydraulic controlsystem during extension and retraction of the hydraulic cylinder 20 isshown in FIGS. 40 and 41 respectively. In FIGS. 40 and 41, the activelines of the hydraulic control system are shown in bold with the valvedrain lines being indicated by dotted lines and the active valve pilotpressure lines being indicated by dashed lines. Also, in FIGS. 40 and41, arrows at each of the active ports indicate hydraulic fluid flowinto and out of the hydraulic control system.

Referring now to FIG. 40, during extension of the hydraulic cylinder 20,pressurized hydraulic fluid is first directed into the hydraulic controlsystem 84 through port A. The hydraulic fluid is directed to a pressurereducing valve 86 which is located in a backpressure line that connectsthe extend and retract lines 90, 92 of the hydraulic control system. Thepressure reducing valve 86 reduces the inlet pressure from a standardsupply pressure (e.g., about 3000 psi) to a predetermined lower pressure(e.g., about 800 psi). From the pressure reducing valve 86, thehydraulic fluid is directed through a check valve 94 and back pressureline 88 that permits the flow of hydraulic fluid into the retract line92 (which during cylinder extension is the return to tank line) at thepredetermined reduced pressure (e.g., approximately 800 psi).

From port A, hydraulic fluid is also directed to a sequence valve 96located in the extend line 90 after passing through a bypass line 98around a check valve 100 that blocks flow from port A. The bypass line98 includes an orifice 102 which restricts or throttles the rate ofhydraulic fluid flow into the extend line 90. In the illustratedembodiment, the hydraulic fluid flow into the extend line 90 isthrottled because the trucks on which the rear eject body 12 wouldtypically be mounted produce flow rates into the hydraulic controlsystem 84 that are higher than needed for the hydraulic cylinder 20 tohandle. Of course, if the fluid flow rate produced by the truck is inthe range that is needed by the hydraulic cylinder 20, the throttlingorifice 102 could be eliminated. The sequence valve 96 is configured toblock the flow of hydraulic fluid into the extend side of the hydrauliccylinder 20 until the pressure reaches a predetermined value. Forexample, the sequence valve 96 can be set to open when the pressurereaches approximately 1000 psi. Thus, until the hydraulic fluid fromport A reaches a pressure of 1000 psi in the extend line 90, all thehydraulic fluid is diverted through the pressure reducing valve 86 andthe backpressure line 88 to produce, in this case, 800 psi ofbackpressure in the retract side of the hydraulic cylinder 20. Thisforces the telescopic sections of the retract side of the hydrauliccylinder 20 to be collapsed or retracted in sequence so that as thehydraulic cylinder 20 is extended, the various hydraulic cylinder stagesextend in the proper sequence and misfiring is prevented.

Once the pressure in the extend line reaches the predetermined value(e.g., 1000 psi), the sequence valve 96 opens allowing hydraulic fluidto flow directly to the extend side of the hydraulic cylinder 20. Thiscauses the hydraulic cylinder 20 to extend. A pressure relief valve 104is provided in communication with the extend line 90 that directshydraulic fluid back to a hydraulic fluid reservoir or tank provided onthe truck through tank line 106 when the pressure in the extend lineexceeds a predetermined value (e.g., 2200-2300 psi) such as at the endof the hydraulic cylinder stroke.

In the meantime, as the hydraulic cylinder 20 extends, hydraulic fluidis being forced out of the retract side of the hydraulic cylinder 20into the retract or return line 92. The check valve 94 in thebackpressure line 88 prevents that hydraulic fluid from flowing backinto the extend line 90 or port A. Instead, the hydraulic fluid forcedout of the retract side of the hydraulic cylinder 20 as it extends, isdirected to a counterbalance valve 108 in the retract line 92. Thecounterbalance valve 108 blocks the flow of hydraulic fluid to port B orback to tank until the pressure reaches a predetermined value, forexample 1000 psi. Once the hydraulic pressure in the retract line 92exceeds the predetermined value (e.g., 1000 psi), the counterbalancevalve 108 opens and allows hydraulic fluid flow to a pressure operatedcheck valve 110. The pressure operated check valve 110 opens based on apilot pressure signal from the extend line 90 through pilot line 112.When the pressure operated check valve 110 is opened, the hydraulicfluid can flow to the tank or reservoir through port B. A check valve114 is arranged in the retract line 92 between port B and the pressureoperated check valve 110. However, the check valve 114 is oriented toallow unrestricted hydraulic fluid flow back to port B. In FIG. 40,lines 116, 117, 119 and 121 are test lines for pressure points at whichthe hydraulic fluid pressure could be tested during extension of thehydraulic cylinder 20.

In sum, when hydraulic fluid is applied to the hydraulic control systemin order to extend the hydraulic cylinder 20, pressure first builds inthe retract line 92 to 800 psi. When the pressure in line 90 exceeds1000 psi, the sequence valve 96 opens and allows the hydraulic fluid toflow to the extend side of the hydraulic cylinder 20. The pressurerelief valve 104 directs the hydraulic fluid back to the tank if thepressure in the extend line 90 exceeds the predetermined value to whichthe relief valve 104 is set. The retract line 92 builds to a pressure of1000 psi and then the counterbalance valve 108 opens and allowshydraulic fluid to flow back through port B to the tank.

Referring now to FIG. 41, when the hydraulic cylinder 20 retracts,hydraulic fluid enters through port B and is directed through theretract line 92 to the check valve 114. This check valve 114 is orientedto block the flow of hydraulic fluid from port B so that the hydraulicfluid is directed through a bypass line 118. The bypass line 118includes an orifice 125 that restricts the flow of hydraulic fluid intothe retract side of the hydraulic cylinder 20. The hydraulic fluid thenflows to the pressure-operated check valve 110, which is a one-way checkvalve oriented to allow unrestricted flow from port B through to thecounterbalance valve 108. A bypass line 120 is provided around thecounterbalance valve 108. The bypass line 120 includes a check valve 122that permits unrestricted hydraulic fluid flow from port B to reach theretract side of the hydraulic cylinder 20 (during extension of thehydraulic cylinder, the check valve 122 blocks flow towards port Bforcing the hydraulic fluid through the counterbalance valve 108). Apressure relief valve 124 is provided in communication with the retractline 92 which directs the hydraulic fluid back to the tank through thetank line 106 when the pressure in the retract line 92 exceeds apredetermined value (e.g., 2300-2400 psi) such as at the end of thehydraulic cylinder retraction stroke.

Since the piston area found in the extend side of the hydraulic cylinder20 is substantially greater than the piston area found in the retractside (e.g., approximately seven times greater), when the cylinder isbeing retracted the hydraulic fluid that is being pushed out of theextend side of the hydraulic cylinder 20 must be allowed to return tothe tank in a fairly unrestricted manner. Accordingly, as hydraulicfluid is flowing to the retract side of the hydraulic cylinder 20, apair of pressure operated check valves 128, 130 in the tank line 106open based on a pilot pressure signal from the retract line 92 throughpilot line 132. The opening of these pressure-operated check valves 128,130 allows unrestricted flow of oil from the extend side of thehydraulic cylinder 20 to the tank. At the same time, the hydraulic fluidfrom the extend side can, also flow via the extend line back to port Aand on to the tank. In particular, the flow in the extend line 90 backto port A proceeds through a check valve 134 in a bypass line 136 aroundthe sequence valve 96 and through the check valve 100 arranged parallelto the bypass line 98 with the flow restricting orifice 102. Both ofthese check valves 134, 100 are arranged to allow unrestricted hydraulicfluid flow back to port A. In FIG. 41, lines 116, 117 and 138 are testlines for pressure points at which the pressure could be tested duringretraction of the hydraulic cylinder 20.

When the hydraulic cylinder is being retracted, the hydraulic fluid flowfrom the extend side of the hydraulic cylinder 20 back to the tankshould be unrestricted in order to prevent backpressure in the extendside of the hydraulic cylinder 20 from stalling retraction of thehydraulic cylinder 20. In particular, because of the much larger pistonarea on which the extend side pressure acts as compared to the retractside pressure, even a minimal back pressure in the extend side canoffset the retract pressure and stall the hydraulic cylinder 20. Forexample, the ratio of the extend side area to the retract side area canbe approximately 8:1. Thus, any backpressure in the extend side of thehydraulic cylinder 20 is multiplied by a factor of 8 when determiningthe force that is being applied against the retract pressure. In such acase, a pressure of 2400 psi in the retract side can be offset by abackpressure of only 300 psi in the extend side of the hydrauliccylinder 20, effectively stalling retraction of the hydraulic cylinder20. With the illustrated hydraulic control system, when retracting thehydraulic cylinder 20, the pressure operated check valves 128, 130 allowa free unrestricted flow of oil out of the extend side of the hydrauliccylinder 20 and back to the tank, thereby minimizing the backpressure inthe extend side of the cylinder 20.

Optionally, instead of utilizing the illustrated tailgate actuationsystem 50, movement of the tailgate 16 between the open and closedpositions can be effected by one or more tailgate cylinders.Advantageously, the hydraulic control system 84 can be modified to alsocontrol the extension and retraction of these tailgate cylinders asshown in FIGS. 42 and 43. In this case, the tailgate cylinders arearranged such that retraction of the tailgate cylinders opens thetailgate 16. Thus, in order to move the tailgate 16 into the openposition when the hydraulic cylinder 20 is extended, the common retractline 140 for the tailgate cylinders is connected to the extend line 90for the hydraulic cylinder 20.

To ensure that the tailgate 16 opens early in the eject cycle, theretract line 140 for the tailgate cylinders is tied into the extend line90 of the hydraulic cylinder 20 before the sequence valve 96. Moreover,the sequence valve 96 can be set to a higher pressure setting. Forexample, the sequence valve could be set to open at 2300 psi as comparedto a 1000 psi setting used when the hydraulic control system 84 onlycontrols the hydraulic cylinder 20. Until the sequence valve 96 opens,the flow of hydraulic fluid to the extend side of the hydraulic cylinder20 is blocked and pressure builds in the retract side of the tailgatecylinder causing the tailgate 16 to open. The hydraulic fluid that isforced out of the extend side of the tailgate cylinders flows through atailgate cylinder extend line 142 that ties into the tank line 106upstream of the relief valve 124. Since the hydraulic fluid in theretract side of the hydraulic control system 84 is not at a high enoughpressure to open the relief valve 124, the hydraulic fluid from theextend side of the tailgate cylinders travels through a check valve 152in a bypass line 150 around the sequence valve 144 and builds asbackpressure in the retract line 92 of the hydraulic cylinder 20 untilthe counterbalance valve 108 opens allowing the fluid to return to tankthrough port B.

Alternatively, as shown in FIG. 43, the hydraulic control system can beconfigured such that a bypass line 154 is provided around the reliefvalve 124. The hydraulic fluid from the extend line 142 flows into thebypass line 154 to a pressure operated check valve 156 that opens basedon a pressure signal from a pilot line 158 connected to the cylinderretract line 140. When the pressure operated check valve 156 is opened,the hydraulic fluid flows to the tank through line 106.

During retraction of the hydraulic cylinder 20, the sequence valve 144blocks the flow of hydraulic fluid into the extend side of the tailgatecylinders until the pressure in the hydraulic cylinder retract line 92reaches a predetermined pressure. In particular, the sequence valve 144is set to open at pressure lower than the relief valve 124 pressuresetting. When the pressure in the hydraulic cylinder retract line 92reaches the predetermined pressure, the sequence valve 144 opensallowing hydraulic fluid to flow into the extend line 142 of thetailgate cylinder, causing the tailgate 16 to close. The sequence valve144 thus delays the closing of the tailgate 16 until the ejector blade18 has started moving towards the retracted position. The hydraulicfluid that is forced out of the retract side of the tailgate cylindersflows through the tailgate cylinder retract line 140 into the hydrauliccylinder extend line 90 and from there back to the tank through port A.

As will be appreciated, the hydraulic control system 84 can be made froman aluminum block that is machined, drilled and tapped accordingly. Thespecifics regarding the pressure settings of the various valve assemblycomponents are only provided as examples and are not intended to limitthe invention in any way.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventor for carrying out the invention. Ofcourse, variations of those preferred embodiments will become apparentto those of ordinary skill in the art upon reading the foregoingdescription. The inventor expects skilled artisans to employ suchvariations as appropriate, and the inventor intends for the invention tobe practiced otherwise than as specifically described herein.Accordingly, this invention includes all modifications and equivalentsof the subject matter recited in the claims appended hereto as permittedby applicable law. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by theinvention unless otherwise indicated herein or otherwise clearlycontradicted by context.

1-11. (canceled)
 12. A rear eject body for a truck comprising: a floor,a pair of opposing sidewalls, a tailgate extending between the opposingsidewalls at a rear end of the rear eject body, the tailgate beingpivotally supported for movement between an open position and a closedposition, an ejector supported in the rear eject body for movementbetween a retracted position at a forward end of the body and anextended position at the rear end of the body, and a tailgate actuationassembly for moving the tailgate between the open and closed positionsin response to movement of the ejector between the retracted andextended positions, the tailgate actuation assembly: (a) linking thetailgate and the ejector when the ejector blade is in the retractedposition thereby holding the tailgate in the closed position, (b)releasing the tailgate from the ejector as the ejector moves from theretracted position towards the extended position such that the tailgatecan swing freely into the open position, and (c) reestablishing the linkbetween the tailgate and the ejector as the ejector moves from theextended position back to the retracted position thereby pulling thetailgate from the open position back into the closed position.
 13. Therear eject body according to claim 12 wherein the release mechanismreleases the tailgate from the ejector after the ejector has moved apreselected distance towards the extended positions.
 14. The rear ejectbody according to claim 13 wherein the release mechanism is configuredsuch that the preselected distance the ejector moves toward the extendedposition before the tailgate is released from the ejector can beadjusted.
 15. The rear eject body according to claim 12 wherein thetailgate actuation assembly includes a release rod connected to thetailgate and having a pivotable lever supported thereon, the pivotablerelease lever being engaged with the ejector when the ejector is in theretracted position and being arranged to pivot out of engagement withthe ejector when the release lever engages a quick release dog supportedon one of the sidewalls of the rear eject body as the ejector moves fromthe retracted position to the extended position thereby permitting therelease rod and release lever to move rearward past the ejector.
 16. Therear eject body according to claim 15 wherein the release rod andrelease lever move rearward after the release lever is disengaged fromthe ejector until the release rod engages a stop surface at which pointthe tailgate is in the open position.
 17. The rear eject body accordingto claim 16 wherein the release lever is oriented to reengage theejector when the ejector moves from the fully extended position back tothe fully retracted position and the quick release dog is pivotallysupported on the sidewall of the rear eject body so as to allow therelease lever to move with the ejector forward past the quick releasedog.
 18. The rear eject body according to claim 17 wherein the quickrelease dog is arranged a distance rearward from the forward end of therear eject body.
 19. The rear eject body according to claim 18 whereinthe sidewall is configured such that the distance the quick releaselever is from forward end of the rear eject body can be adjusted. 20.The rear eject body according to claim 15 wherein the release rod isconnected to a flexible link that connects to the tailgate, the flexiblelink acting around a drum for pulling the tailgate from the open to theclosed position.
 21. The rear eject body according to claim 20 whereinthe drum has a radius of curvature that varies such that the moment armon which the flexible link acts with respect to the tailgate is greatestwhen the tailgate is in a horizontal position and relatively less whenthe tailgate is in the relatively more vertical open and closedpositions.
 22. The rear eject body according to claim 12 furtherincluding an ejector guide assembly including a plurality of sledsconnected to the ejector, each sled being received in one of a pair ofguide tracks and each guide track being arranged on an inside surface ofa respective one of the sidewalls, wherein the sleds slide in guidetracks and thereby guide the ejector as the ejector moves between theretracted and extended positions.
 23. A rear eject body for a truckcomprising: a floor, a pair of opposing sidewalls, a tailgate extendingbetween the opposing sidewalls at a rear end of the rear eject body, thetailgate being pivotally supported for movement between an open positionand a closed position, an ejector supported in the rear eject body formovement between a retracted position at a forward end of the rear ejectbody and an extended position at the rear end of the rear eject body,and a tailgate actuation assembly for moving the tailgate between theopen and closed positions in response to movement of the ejector betweenthe retracted and extended positions, the tailgate actuation assemblyincluding a flexible link connected to the tailgate that acts around adrum for pulling the tailgate from the open to the closed position, thedrum having a radius of curvature that varies such that the moment armon which the flexible link acts with respect to the tailgate is greatestwhen the tailgate is in a horizontal position and relatively less whenthe tailgate is in the relatively more vertical open and closedpositions.
 24. The rear eject body according to claim 23 wherein thetailgate actuation assembly links the tailgate and the ejector when theejector is in the retracted position thereby holding the tailgate in theclosed position, releases the tailgate from the ejector as the ejectormoves from the retracted position towards the extended position suchthat the tailgate can swing freely into the open position, andreestablishes the link between the tailgate and the ejector as theejector moves from the extended position back to the retracted positionthereby pulling the tailgate from the open position back into the closedposition.
 25. A rear eject body for a truck comprising: a floor, a pairof opposing sidewalls, an ejector supported in the rear eject body formovement between a retracted position at a forward end of the body andan extended position at the rear end of the body, a hydraulic cylinderfor moving the ejector between the retracted and extended positions, thehydraulic cylinder being configured to extend and thereby move theejector towards the extended position when hydraulic fluid is suppliedto a extend side of the hydraulic cylinder and to retract and therebymove the ejector towards the retracted position when hydraulic fluid issupplied to a retract side of the hydraulic cylinder, and a hydrauliccontrol system for controlling the flow of hydraulic fluid to the extendand retract sides of the hydraulic cylinder, the hydraulic system beingconfigured to build backpressure into the retract side of the hydrauliccylinder before hydraulic fluid is allowed to flow to the extend side ofthe hydraulic cylinder to initiates extension of the hydraulic cylinder.26. The rear eject body according to claim 25 wherein the hydrauliccontrol system allows the flow of hydraulic fluid out of the retractside of the hydraulic cylinder to a hydraulic fluid tank when thebackpressure in the retract side of the hydraulic cylinder reaches apredetermined value.
 27. The rear eject body according to claim 25wherein the hydraulic control system throttles the flow of hydraulicfluid to the extend side of the hydraulic cylinder.
 28. The rear ejectbody according to claim 25 wherein the hydraulic control system allowsthe flow of hydraulic fluid out of the extend side of the hydrauliccylinder and back to a hydraulic fluid tank when the pressure in theextend side of the hydraulic cylinder exceeds a predetermined value. 29.A rear eject body for a truck comprising: a floor, a pair of opposingsidewalls, an ejector supported in the rear eject body for movementbetween a retracted position at a forward end of the body and anextended position at the rear end of the body, a hydraulic cylinder formoving the ejector between the retracted and extended positions, thehydraulic cylinder being configured to extend and thereby move theejector towards the extended position when hydraulic fluid is suppliedto a extend side of the hydraulic cylinder and to retract and therebymove the ejector towards the retracted position when hydraulic fluid issupplied to a retract side of the hydraulic cylinder, and a hydrauliccontrol system for controlling the flow of hydraulic fluid to and fromthe extend and retract sides of the hydraulic cylinder, the hydraulicsystem being configured to allow hydraulic fluid flow out of the extendside of hydraulic cylinder through a line connecting the extend side ofthe hydraulic cylinder directly to a hydraulic fluid tank when hydraulicfluid is being supplied to the retract side of the hydraulic cylinderduring retraction of the hydraulic cylinder and the pressure in theretract side of the hydraulic cylinder reaches a predetermined value.30. The rear eject body according to claim 29 wherein the hydrauliccontrol system allows the flow of hydraulic fluid out of the retractside of the hydraulic cylinder and back to a hydraulic fluid tank whenthe pressure in the retract side of the hydraulic cylinder exceeds apredetermined value.
 31. A rear eject body for a truck comprising: afloor, a pair of opposing sidewalls, an ejector supported in the reareject body for movement between a retracted position at a forward end ofthe body and an extended position at the rear end of the body, anejector hydraulic cylinder for moving the ejector between the retractedand extended positions, a tailgate extending between the opposingsidewalls at a rear end of the rear eject body, the tailgate beingpivotally supported for movement between an open position and a closedposition, a tailgate hydraulic cylinder for moving the tailgate betweenthe open and close positions, and a common hydraulic control system forcontrolling the flow of hydraulic fluid to and from both the ejectorhydraulic cylinder and the tailgate hydraulic cylinder. 32-35.(canceled)
 36. A rear eject body for a truck comprising: a floor, a pairof opposing sidewalls, and an ejector supported in the rear eject bodyfor movement between a retracted position at a forward end of the reareject body and an extended position at the rear end of the rear ejectbody, the ejector having a lower face that angles upward away from thefloor as the lower face extends toward the forward end of the rear ejectbody, an upper face that angles downward toward the floor as the upperface extends toward the forward end of the rear eject body and a pair ofopposing side faces wherein each side face angles inward away from thesidewalls as the side face extends towards the forward end of the reareject body.